The present invention relates to an improved annulus valve for concentric tubing hangers. Valves have been known in the past to provide a means of closing the passage through a tubing hanger which provides communication of the annulus below the hanger with the annulus above the hanger. Such valves have included a check valve which is biased toward closed (upper) position by a spring and includes an integral rod extending upwardly above the hanger so that when the xmas tree mandrel is landed a plate thereon engages the upper end of the rod and causes the rod to move the valve member downwardly against spring force to thus unseat the valve and provide communication through the hanger passage. Such prior art valves have been deemed to be unsafe because on landing the tree the valve is opened before the tree connector can be locked to the wellhead housing and tested. This creates a potential hazard when there is gas under pressure in the annulus below the hanger. Additionally the valve cannot be closed and tested before pulling the tree. If the valve is going to fail to shut, this should be known in advance so that the annulus can be killed before pulling the tree.
Another type of valve known in the past is a valve which includes an inner sleeve for opening and closing flow through the hanger and the valve is spring-loaded, pressure-assist to close design, with parallel seals closing off a side outlet port from the annulus bore. The valve is maintained open by a constant pressure from the control circuitry in production mode. The valve can be tested for effective closure before pulling the tree but it requires extra umbilical/production control system cost and also the annulus communication is lost in the event of control line failure.
Still another type of shut-off mechanism includes an electrical connector. These types of systems require multiple additional control functions in the production mode which is economically disadvantageous in comparison to a dual-bore tubing hanger system.
U.S. Pat. No. 3,360,048 discloses a structure in which the flow through a hanger from its annulus is controlled by a sleeve valve operated by a wireline tool.
U.S. Pat. No. 4,449,583 discloses an annulus spring check valve and a pressure fluid by-pass. It is proposed that the check valve can be opened and communication established through the by-pass by a handling tool through a stabbing operation or by pressure on the check valve delivered via the production upper body.